1. Field of the Invention
The present invention relates to a preferable map display applied to a map display for displaying a position by utilizing a positioning system called GPS (Global Positioning System) for which satellites are used.
2. Description of the Related Art
Conventionally, various receivers for a positioning system called GPS for which satellites are used have been developed. Positioning by using this receiver is receiving positioning signals sent from a plurality of (about 24) artificial satellites orbiting the earth, demodulating information included in the positioning signals from the respective satellites, analyzing the information obtained by the demodulation, and carrying out positioning of a present position. In this case, the information included in the positioning signals sent from the respective satellites include time data of the satellites, orbit data for calculating positions of the satellites, and the like. The positioning signals including the information are sent after they are spread-spectrum modulated and quadrature-phase modulated by two carrier waves (two-phase PSK modulation). The same frequencies (1227.6 MHz and 1575.42 MHz) are used for all the satellites as frequencies of the two carrier waves and a code used for spread-spectrum modulation is different for each satellite.
Then, in positioning, the positioning signals are received at the same time from at least three satellites, the information included in the received positioning signals from the three satellites is demodulated, the demodulated information is analyzed, and a processing for positioning an absolute position such as longitude, latitude, and the like is carried out.
Various navigation systems for displaying a map of a vicinity of the present position by using such a system for carrying out positioning of the absolute position by the GPS have been developed. As the navigation system, there are a vehicle-mounted system mounted to a mobile body such as an automobile and a small-sized system formed for a carrying purpose.
Here, in the case of the vehicle-mounted navigation system, it is possible to carry out navigation by preparing a mass-storage device (e.g., an optical-disc playback device such as CD, DVD, and the like) in which electronic map data over a relatively wide range is stored and displaying the map of the vicinity of the present position read out from the storage device on a display connected to the storage device. On the other hand, in the case of the small-sized navigation system for the carrying purpose, if the mass-storage device is built into the system, a size of the system is increased and portability is impaired. Therefore, it is not preferable to build the mass-storage device in the system.
Therefore, it has been proposed to carry out navigation in the vicinity of the present position by combining a map displayed in a form of a printed map, for example, and position display by the navigation system. For example, it has been proposed to prepare a map printed on a transparent sheet in advance and to put the prepared map sheet on a display panel of the navigation system such that a position displayed on the display panel is displayed on the map.
However, in the case of the prior-art navigation system for which the map in the form of the printed map is used, only the maps prepared especially for the navigation system can be used. In other words, if the map does not have a scale, longitude, and latitude in preset states, the map does not correspond to the position display on the display panel of the navigation system, and therefore, accurate navigation cannot be carried out. Therefore, even though the navigation system itself is small-sized for the carrying purpose, it is necessary to carry the special maps with the system, and the system is not preferable as a portable system.
In view of the above points, it is an object of the present invention to make any maps usable for navigation.
To achieve the above object, according to the present invention, there is provided a map display comprising display means for displaying read map image data, input means for designating an absolute position obtained by positioning by positioning means on a map displayed on the display means, and control means for calculating positions on the map corresponding to the absolute positions obtained by positioning by the positioning means based on the absolute positions of at least two points on the map designated by the input means and for displaying the calculated positions on the map displayed by the display means.
According to the invention, the absolute coordinates positions of at least two points in the read map image data can be obtained by designation by the input means. Based on the relationships among the coordinates positions of the two points and the present position obtained by positioning by the positioning means, it is possible to judge to which point in the map image data the present position corresponds and to display the judged present position on the map.